Just a couple of weeks ago, Marten Mickos was telling me how great Sun Microsystems’ MySQL database business was performing during the economic downturn. Now, he’s left the company, adding to a string of departures that threaten one of Sun’s fastest-growing businesses.

Sun has confirmed the exit of Mr. Mickos, the chief executive of MySQL before Sun acquired it for $1 billion last year, and Monty Widenius, another MySQL co-founder. Last October, David Axmark, yet another MySQL co-founder, left Sun as well.

In a blog post, Mr. Widenius, the original developer of MySQL, chastised Sun for moving at a slow pace with the open source software’s development -– a criticism that crops up time and again about various Sun businesses.

It’s not unusual for the leaders of an acquired company to jump ship. Often, entrepreneurial personalities fail to mesh with the stodgier cultures of large corporations.

But the loss of the core MySQL team bodes ill for Sun, which pushes the open source database as an alternative to similar products from Oracle, Microsoft and others. Much of Sun’s future hinges on its ability to turn the open-source MySQL and its open-source Solaris operating system into must-have business software that then drives interest in Sun’s hardware products.

For a company facing a multiyear decline in hardware sales, Sun needs all of its engines humming along smoothly.

Sun’s track record at absorbing acquired companies is spotty at best. It’s enjoyed some huge wins around acquired hardware products like its high-end server line and multicore chips. Over all, however, Sun has proved inept at turning acquired hardware and software technology into profitable product lines and at retaining talent.

The teams at companies like Terraspring, Cobalt Networks and CenterRun, for example, scurried away from Sun, often ending up at start-ups that went on to compete against the company. In addition, Sun’s efforts to revitalize its storage business by buying the start-up Pirus and the tape giant StorageTek have failed.

When we last talked, Mr. Mickos insisted that companies continued to obtain MySQL at a rate of about 65,000 downloads per day. It’s an astonishing figure, but one that does little for Sun’s bottom line. Sun must still convert those free downloads into customers willing to pay for support and buy the company’s hardware.

In its last quarter, Sun stated that its infrastructure software business increased 55 percent year over year. But the revenue remains low at $81 million.

Sun has now lost the business and spiritual leaders that turned MySQL into a success, and it will be up to Karen Tegan Padir, the new vice president in charge of the infrastructure software business, to make sure Sun avoids spoiling another acquired asset.